The long-term objective of this study is to develop a new surgical procedure, endoscopic cyclophotocoagulation, for the treatment of difficult cases of glaucoma. The specific aim of this pilot study is to evaluate techniques for effective destruction of individual ciliary processes, without damage to adjacent tissue, using intraocular laser with endoscopic visualization. It is hoped that this investigation will provide information necessary for further laboratory and eventual clinical evaluations, ultimately leading to a procedure for controlling certain forms of glaucoma for which there is currently no completely satisfactory treatment. The instrument to be evaluated in the pilot study will be made from a commercially available, direct-viewing endoscope (Needlescope, Dyonics, Inc.) with an intraocular laser probe attached to the shaft of the endoscope. Six rhesus monkeys will he used in the study. In preliminary trials primates were found to be a preferable model for the experiments in this study. In addition, the similarity of the anatomy to human ciliary processes allows better application of the results to future clinical studies. A lentectomy and an anterior vitrectomy will be performed on one eye of each animal. The endoscope-laser probe will then be inserted through the same pars plana incision, and laser energy will be applied to clusters of individual ciliary processes 180 degrees from the entry site under direct visualization with the endoscope. Laser power settings and the position of the probe tip in relation to the ciliary processes will be varied for different clusters of processes. These data and the immediate appearance of the tissue response to the laser application will be recorded for subsequent correlation with histologic observations. Two animals each will then be followed with weekly examinations for one, three, and six months. The laser procedure will be performed on the fellow eye of one animal at the end of each follow-up period, and both animals will be killed at that time. The eyes will then be enucleated and studied by light microscopy to correlate the degree of early and late tissue damage with the specific techniques of laser application and the immediate appearance of the ciliary process. The three untreated eyes will serve as normal controls.